The present invention relates generally to fluid pumps, and particularly, to a lubrication pump capable of providing a substantially constant outflow of fluid.
As is well-known to those skilled in the art of automotive vehicle, but also known by those in other arts, mechanical assemblies often require fluid lubrication for optimal performance and reliability. Typical examples where this need for lubrication is especially important in automotive vehicles include piston engines, transmissions, and other drivetrain components. Commonly, lubrication is provided to these components with a fluid pump that produces an outflow of fluid from a fluid reservoir. The outflow of fluid is then directed throughout the component that requires lubrication by a number of narrow passages or hoses.
To optimize lubrication, the fluid is often routed directly to critical friction surfaces within the component. Typically, these critical friction surfaces involve mating metal surfaces that slide against each other under high speed or high load. A common example of a critical friction surface that requires lubrication is the journal and bearing surface of a rotating bearing. Lubrication of moving parts generally provides two benefits. First, the fluid minimizes wear between the moving parts, thus lengthening the operating life of the component and also increasing efficiency of the component. Second, the fluid absorbs heat that is generated by the friction between the moving parts, thus dissipating the heat away from the moving parts and cooling the component. As is well-known by those in the art, a variety of fluids can be used to lubricate critical friction surfaces, and the choice is usually influenced by a number of different design considerations. Petrochemical oils with varying viscosities are commonly used for lubrication and are satisfactory for many applications. One example of a well-known and often used lubricant is automatic transmission fluid, or also referred to as Dextron II.
Traditionally, lubrication of automotive vehicle components has been provided by mechanically driven fluid pumps. Accordingly, the fluid pump is usually mounted directly to or close by the drivetrain component, and power is provided to the pump from rotating drive members in the component. A variety of drive systems have been employed to power lubrication fluid pumps, with one common example including an input drive shaft that extends into the fluid pump and a gear from the drivetrain component that drives the input drive shaft.
One characteristic of mechanically driven fluid pumps is that the volume of fluid outflow from the pump usually varies as the speed of the input drive shaft varies. Thus, as the speed of the drive gear from the component increases (and consequently the speed of the input drive shaft increases), the volume of fluid flowing from the pump will increase. Similarly, as the speed of the component decreases, the outflow from the pump also decreases. Thus, a proportional relationship generally exists between the speed of the component and the outflow of fluid from the pump.
Usually, this variation in outflow from the pump does not present any significant problems to the performance of an automotive vehicle. Typically, the engine in an automotive vehicle operates within a relatively narrow range of rotational speeds. Thus, the maximum speed of the engine is often about 3,000 rpm and the slowest speed of the engine is about 500 rpm when the engine is idling. The rotational speed of the drivetrain components are likewise relatively narrow. Therefore, because the speed of the input drive shaft for the fluid pump varies within a relatively narrow range, the resulting variation in lubricating fluid flow is also minimal. This limited variation in lubricating fluid flow generally has few adverse effects on the drivetrain components because a range of flow volume is acceptable.
However in some lubricating systems, a proportional relationship between component speed and pump outflow is unsatisfactory. One such example involves electric motor driven drivetrains. In these systems the electric motor can operate at much faster speeds than traditional drivetrain components. In addition, the electric motor can operate at very low speeds below the traditional 500 rpm idling speed, including speeds nearing zero rpm. In these types of drivetrains, the normal variation in outflow from a traditional fluid pump is too large to provide acceptable lubrication of the drivetrain components. The problem is especially acute at low speeds, where the outflow of fluid from a traditional pump is reduced significantly and approaches zero as the electric motor nears zero rpm. In contrast, the electric motor in these systems tends to operate at its worst efficiency and generates the most heat at low speeds. Thus, in drivetrains where the fluid pump is used to lubricate and cool the electric motor in addition to other drivetrain components, a traditional fluid pump is inadequate to provide acceptable fluid flow.
Another problem with mechanically driven fluid pumps is the inability to provide fluid outflow when the rotational direction of the input drive shaft reverses. This is generally not a problem with piston engine drivetrains because the major drivetrain components always rotate in the same direction and never reverse their direction of rotation. However, when an electric motor is used in the drivetrain, the rotational direction of the drivetrain components can easily be reversed by simply switching the direction of rotation of the electric motor through its logic controller. Thus, traditional fluid pumps are also inadequate for electric motor drivetrains because they do not provide lubrication fluid when the electric motor reverses direction.
One alternative to a traditional mechanically driven fluid pump is an electric powered fluid pump. In this alternative, the electrical system of the automotive vehicle supplies power to the fluid pump. The pump and the resulting outflow of fluid can then be controlled by a logic controller. Thus, the fluid outflow can be controlled irrespective of the speed or direction of rotation of the drivetrain. Accordingly, the volume of fluid outflow from the pump can be maintained at a substantially constant volume throughout the entire range of drivetrain component speeds. The electric pump is also unaffected by the rotational direction of the drivetrain, and thus lubrication fluid can be provided when the drivetrain is operated in a reverse direction.
Several problems exist with electric pumps however. Electric pumps generally operate less efficiently than mechanically driven fluid pumps. For example, in mechanically driven pumps the drive system is often about 96% efficient in providing power to the pumping assembly. On the other hand, an electric drive system is usually only about 80% efficient in providing power to the pumping assembly. Electric pumps are also usually less reliable than mechanically driven pumps during the operating life of the automotive vehicle. This lower reliability typically occurs because electric pumps are more complicated, thus providing more potential sources of failures. Electric pumps are also the source of more failures because the electric pump is usually mounted to the chassis of the automotive vehicle and is connected to the drivetrain components with fluid hoses and electrical wiring. As a result, these extra hoses and wires become susceptible to damage from being town, worn or cut. In contrast, mechanically driven pumps are often designed to be integral with a drivetrain component, making excess hoses and wires unnecessary. In addition, another problem with electric pumps is the difficulty of designing an electric pump into the electrical system of an automotive vehicle. Typically, automotive vehicles are provided with a 12V electrical system to power a variety of accessories. If an electric motor drivetrain is used in the automotive vehicle, another higher voltage electrical system may be provided for the electric motor. However, the electric pump is not always easily designed into either of these electrical systems because of load and efficiency considerations. One final problem with electric pumps is their cost, which is usually higher in automotive vehicles than mechanical pumps. As is well-known, automotive vehicles are typically produced by manufacturers in high volumes. As a result, mechanically driven pumps are usually less expensive since the capital cost of designing a specially adapted pump can be averaged across a large number of vehicles.
Accordingly, a mechanically driven fluid pump is provided for producing a fluid outflow that is not proportional to the speed of the input drive. The pump includes a control valve that directs some of the fluid from the pump assembly to an outflow port and some of the fluid to a diversion port. As the speed of the input drive charges, the position of the valve is altered, thus altering the proportion of fluid directed to the outflow and diversion ports. A mechanical governor that applies centrifugal force to swing arms can be used to alter the position of the control valve proportionately to the speed of the input drive.
Two embodiments of a pump assembly are provided with both embodiments capable of producing fluid flow when the rotational direction of the input drive is reversed. One embodiment is an impeller pump assembly that includes an impeller with forward and reverse impeller sections. When the input drive rotates, one of the impeller sections is sealed by a dividing plate, thus producing fluid flow from one of the impeller sections. Another embodiment is a cam piston pump assembly. The cam piston pump assembly includes a cam attached to the input shaft and a pushrod biased against the cam. The pushrod reciprocates a piston which forces fluid through a control valve.